The process control industry employs process variable transmitters to remotely monitor process variables associated with substances such as solids, slurries, liquids, vapors, and gasses in chemical, pulp, petroleum, pharmaceutical, food and other food processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties. A process variable transmitter can provide an output related to the sensed process variable over a process control loop to a control room, such that the process can be monitored and controlled.
The process control loop can be a two-wire, 4-20 mA process control loop. With such a process control loop, the energization levels are low enough that even under fault conditions the loop generally will not contain enough electrical energy to generate a spark. This is particularly advantageous in flammable environments. Process variable transmitters can sometimes operate on such low energy levels that they can receive all electrical power from the 4-20 mA loop. The control loop may also have digital signals superimposed on the two-wire loop according to a process industry standard protocol such as the HART(copyright) digital protocol.
Low power Time Domain Reflectometry radar (LPTDRR) instruments have been used to measure the level of process products (either liquids or solids) in storage vessels. In Time Domain Reflectometry, electromagnetic energy is transmitted from a source, and reflected at a discontinuity. The travel time of the received pulse is based on the media through which it travels. One type of LPTDRR is known as Micropower Impulse Radar (MIR), which was developed by Lawrence Livermore National Laboratory. LPTDRR level transmitters typically determine level (such as level of a fluid in a storage tank) as a function of the time of travel of microwave signals to and from an interface or surface of the product. However, this technology may be used to measure process variables other than level.
An apparatus for measuring concentration of a material in a process fluid includes an antenna configured to contact the process fluid and a pulse generator coupled to configure the antenna to generate a microwave transmit pulse through the antenna. A pulse receiver receives a reflected pulse from the antenna and the concentration of the material is calculated as a function of the reflected pulse.